Feature: A seeded showcase of every element 

Description 

Feature: Seed a page tree from a definition writes a page tree from a YAML definition. The shipped definition EXT:theme_extension_development/Configuration/Seeds/Demo.yaml now describes a tree that demonstrates the whole theme rather than a handful of pages:

Between them the pages use every backend layout the extension registers and carry every content type it renders, so a single seeded instance answers what the theme does with each. Two of the pages are deliberate special cases: Empty page selects no backend layout at all, which is the only way to see the default fallback, and Styleguide is set to Page not enabled in menus rather than disabled - a disabled page returns 404 in the frontend and is only reachable through a preview link, which defeats the point of seeding a page that exists to be opened.

Inline children in the seed format 

Four of the theme's own content elements - Author, Link list, Social links and Media teaser grid - read their entries from an inline child table. A seed definition can now describe those entries with a new structural key, inline: a map of the field on the parent record to the child records declared for it.

content:
  - identifier: showcase-linklist
    CType: theme_linklist
    header: 'Where to read more'
    inline:
      tx_theme_list_items:
        - identifier: showcase-docs
          table: tx_theme_list_item
          link: 't3://page?uid=2'
          link_label: 'Typography'
        - identifier: showcase-media
          table: tx_theme_list_item
          link: 't3://page?uid=3'
          link_label: 'Media'

Each child names the table it belongs to. That is never inferred from the TCA of the parent's field, so a definition stays readable on its own and a mistyped field name is reported rather than dereferenced. The children come out in the order they are declared, and they may carry uid and files like any other record.

The structural keys of the format are therefore identifier, uid, children, content, files and inline, plus table on an inline child. Everything else is a field of the record and is written as it stands - which is why the backend layout and the "hide in menus" flag of the pages above need nothing from the seeding at all.

Identifiers may no longer contain an underscore 

An identifier in a seed definition may contain letters, digits and dashes, and has to start with a letter or a digit. A definition using anything else is now rejected with an exception naming the identifier.

This is not a style rule. The identifier ends up inside the placeholder DataHandler is given for the record, and a placeholder used as the value of a relation field is read as the <table>_<uid> form when it contains an underscore - so NEWtt_content_home is split into a table NEWtt_content and an id home, neither of which resolves. The relation is then written empty, with nothing logged. Rejecting the identifier is what turns a seed that silently loses its relations into one that refuses to run.

Two fixes come with it 

Both failed silently, and both are now covered by a regression test:

• A declared uid was not honoured. DataHandler reads a suggested uid from the data map row and looks it up under a <table>:<uid> key; the seeding supplied neither, so the next free uid was assigned and the command reported whatever it got. That looked correct only for as long as the declaration order of a definition happened to match its insertion order.
• File references were not ordered. The placeholder of a reference had the same underscore problem, so sorting_foreign stayed at 0 on every seeded reference and the order of a gallery with more than one image was left to the database.

Known limitation 

Categorized pages and Categorized content are part of the seeded tree but select nothing: the format expresses neither sys_category records nor the MM rows relating them to a page or a content element. Both elements render an empty menu, which is the correct rendering of "no category chosen". Supporting this needs a way to declare records outside the page tree and a relation between two of them, which is out of proportion to demonstrating two elements.

Impact 

vendor/bin/typo3 theme:seed produces a frontend that exercises the theme end to end, so a development or test instance no longer needs pages built by hand to see what an element looks like. Definitions of your own can describe inline relations, and have to use identifiers without underscores.